1. Field of the Invention
This invention relates to a planar radiating oscillator apparatus for micro- and millimeter waves that integrates electromagnetic wave radiation antenna and high-frequency wave oscillation capabilities, is usable in high-efficiency microwave submillimeter-region telecommunication apparatus and radiometry technologies, and can be used as a spatial power combining type oscillator apparatus for high-power output.
2. Description of the Prior Art
Conventional radio equipment, including radio communication apparatuses and various types of radiometry equipment such as radar systems and radiometers, is configured by combining antenna apparatus technologies and transmitter/receiver technologies related mainly to high-frequency circuitry. Antenna apparatus technologies for efficiently radiating electromagnetic waves and receiving electromagnetic wave signals in accordance with the intended purpose and high-frequency circuit technologies for the transmitters and receivers that handle signal processing and control have long constituted mutually independent fields of technology that meet only in the need to match the antenna input and circuit output impedances.
The telecommunication equipment technology sector is undergoing major changes. Recent advances in semiconductor device technology have led to the development of technologies that make it possible for amplifier, oscillator, multiplier, mixing and other high-frequency circuit element functions to be achieved by integrated planar circuits. These high-frequency integrated circuit technologies are being widely viewed as providing radio communication apparatus technologies of the future that will enable apparatuses whose integrated, planar circuitry makes them simultaneously light, compact, high-performance, highly reliable and low cost. As such, they can be expected to be used in place of the conventional type of system of configuring apparatuses by interconnecting waveguide and coaxial circuit components. This technological environment is creating a need for the development of new micro- and millimeter wave technologies that can integrate the antenna with the integrated circuitry. The progress in semiconductor device technology for high-frequency circuit applications is generating demand for a broad range of technologies. These include technologies able to provide the new device functions needed to configure micro- and millimeter wave mobile communication systems, as well as technologies for providing radiometry control systems with new capabilities such as high-function antenna beam shaping techniques and micro- and millimeter wave imaging techniques.
As frequencies rise in the micro- to millimeter wave region, dielectric loss and conductor loss at the conductor surface increase to pose a major problem in terms of transmission line loss. Arraying planar antennas to enhance antenna gain results in a heavy feeder loss and a large drop in system total performance and efficiency from the connections in the long transmission line of the micro- and millimeter wave radio apparatus. While there is therefore a considerable need to develop a new technology for integrating the antenna and the high-frequency planar circuit, numerous difficult technical problems remain to be solved before this can be done.
In the simplest configuration, with the active circuit and the antenna circuit disposed adjacently on the same plane, it is difficult with high-frequency coupling to realize the desired apparatus functions by the antenna pattern, oscillator frequency, deviation of noise characteristics and the like. While rigorous consideration of spatial intercoupling methods is required in such cases, these are generally complex and, except in special cases, usually difficult to solve by electromagnetic field analysis.
As is clear from the foregoing, in order to realize transmitter technologies able to efficiently effect high-frequency generation and output and impart objective-matched directionality for radiation in the required direction, it is necessary to develop a new method for functionally integrating the oscillator circuit and the antenna with high efficiency. An insufficiently high amplitude of the high-frequency signal to be transmitted to a desired location has conventionally been coped with either by increasing the output of the signal source or by increasing the antenna gain.
A multi-element antenna array with a sharp antenna radiation characteristic can be achieved provided that a signal source can be readily obtained that has sufficiently high output to compensate for the drop in radiation efficiency caused by the feeder loss. However, the fact that millimeter wave semiconductor devices are fabricated using ultrafine processing technologies to provide the fine geometries needed to secure high-frequency characteristics means that the power that individual devices can handle falls sharply with increasing frequency. Thus, finding ways to achieve an adequate output in the millimeter wave region is an important focus of technical research.
FIG. 19 is a view representing the configuration of a conventional high-frequency oscillator apparatus. In this arrangement, a resonator 1 and negative resistance amplifier circuit 2 are coupled by a waveguide 4 and a load 3 is attached to other terminals of the negative resistance amplifier circuit 2 via a waveguide 5. In this configuration, oscillation power is extracted from a port separate from the resonator 1. In this oscillator apparatus configuration, which is used extensively for portable telecommunication devices operating in the microwave and submicrowave frequency ranges, the resonator 1 incorporates a dielectric resonator that is compact and has a high dielectric constant.
In contrast, in the conventional oscillator apparatus configuration illustrated in FIG. 20, the resonator also functions as an electromagnetic wave output section. In this arrangement, a negative resistance amplifier circuit 2 is incorporated inside a resonator 1 and a load 3 represents the amount of additional loss caused by extraction of the oscillation power to the resonator exterior. A typical example of such a configuration is that of a laser oscillator provided with an amplification medium inside its resonator. In this configuration load 3 represents the extraction of the oscillation power in the form of a beam radiating into free space from a partially transparent reflecting mirror surface of the laser resonator.
FIG. 21 is a view illustrating another configuration of a conventional radiating oscillator apparatus in which the resonator also functions as an electromagnetic wave output section. In this arrangement a resonator 1 and negative resistance amplifier circuit 2 are connected by a waveguide 4, and a load 3 represents the amount of additional loss caused by extraction of the oscillation power to the resonator exterior as a beam 5. In one example of such a configuration, one of the present inventors has disclosed a micro- and millimeter wave oscillator apparatus that integrally combines a Gaussian-beam resonator with a negative resistance amplifier circuit (U.S. Pat. No. 5,450,040). In terms of principle, the oscillator apparatus of FIG. 21 is a variation of the configuration of FIG. 20 in which the extraction of the amplification medium to the outside of the resonator is advantageous in terms of the oscillator apparatus technology in that it enables the securing of two parameters that make it possible to control the oscillation conditions.
FIG. 22 illustrates the configuration of a conventional beam output type micro- and millimeter wave oscillator apparatus that is a specific embodiment of the configuration of FIG. 21. Here, the resonator 1 of FIG. 21 is a Fabry-Perot resonator 8 comprised of a spherical, partially transparent reflecting mirror surface 6 and a conductor reflecting mirror surface 7 in which a negative resistance amplifier circuit 2 is connected by a waveguide 4 and a coupling region 9 that constitutes part of the conductor reflecting mirror surface 7 of the resonator 8. The partially transparent reflecting mirror surface 6 may be constituted by a two-dimensional conductive thin-film grid. Either the reflecting mirror surface 6 or the conductor reflecting mirror surface 7 may be constituted as a spherical mirror, whereby the resonator mode forms a Gaussian distribution about the optical axis.
Moreover, to configure the resonator as one that is weakly coupled with free space, the reflectance of the reflecting mirror surface 6 is set to be higher than the reflectance of the conductor reflecting mirror surface 7 so that when viewed from the side with the negative resistance amplifier circuit 2, the resonator 8 appears to be a one terminal device. The interaction between the resonator and the negative resistance amplifier circuit 2 increases the oscillation, increasing the high-frequency wave electric power accumulated inside the resonator and also increasing the power of a beam output 10 leaking out as a Gaussian beam from the partially transparent reflecting mirror surface 6, resulting in a steady state of balance between the gain by the negative resistance amplifier circuit 2 and the total loss, which includes the oscillation output.
In the apparatus of FIG. 22, since the reflectances of the partially transparent reflecting mirror surface 6 and the conductor reflecting mirror 7, i.e., the coupling strength with free space, and the coupling strength with the negative resistance amplifier circuit 2 can be set independently, two basic oscillator apparatus adjustment items, including phase adjustment through combination of the coupling region 9 and the waveguide 4, can be substantially controlled. On the other hand, the Gaussian beam resonator is limited in application by the size of its aperture, which is several wavelengths or more. Moreover, it is by nature a high-Q resonator, and as such is not suitable for applications in which wideband frequency characteristics are required.
FIG. 23 illustrates a conventional oscillator apparatus configuration in which the negative resistance amplifier circuit and the antenna elements are disposed adjacently on the same plane. In FIG. 23, a high-frequency transistor 12 is integrated with a resonator 1 composed of a strip line to constitute an oscillator as a negative resistance amplifier circuit, and direct current power supplied from a direct current bias line 11 is converted to high-frequency power and radiated into free space via an integrally connected square conductor patch 15 antenna. Since coupling of the oscillation between a stub 13, the strip line resonator 1, the direct current bias line 11 and the square conductor patch 15 antenna is hard to avoid, slight differences in impedance matching, resonant frequency, wire location and the like produce complex interactions that critically affect frequency spectrum, power output and radiation pattern, making the oscillator apparatus of FIG. 5 difficult to handle in practice.
FIG. 24 shows an example of a prior art radiating oscillator apparatus disclosed by York et al. in which the planar conductor patches serve as both a resonator and as an electromagnetic wave output section (R. A. York and R. C. Compton, "Quasi-Optical Power Combining Using Mutually Synchronized Oscillator Arrays," IEEE Trans. on Microwave Theory and Tech., Vol. MTT-39, pp. 1000-1009, 1991). This disclosure describes a method of configuring a simple planar radiating oscillator apparatus. This comprises adjacently disposing two rectangular conductor patches 15 each formed as a broad low-impedance microstrip line across a narrow gap 16 connecting the drain and gate of a field effect high-frequency transistor (FET) 12 whose source is grounded one to each of the low-impedance microstrip lines, directly biasing the two low-impedance microstrip lines by direct current bias lines 11, and using the capacitive coupling by the narrow gap 16 as an amplifier positive feedback circuit to constitute a negative resistance amplifier circuit as seen from the side of the resonator in terms of high frequency.
FIG. 25 shows another example of a prior art radiating oscillator apparatus in which the planar conductor patches serve both as a resonator and an electromagnetic wave output section (R. A. Flynt, J. A. Navarro and K. Change, "Low Cost and Compact Active Integrated Antenna Transceiver for System Applications," IEEE Trans. Microwave Theory Tech., Vol. 44, pp. 1642 to 1649, 1996). In this arrangement, semicircular conductor patches 17 are arranged in mutual opposition and a high-frequency FET 12 is disposed at the center to configure a radiating oscillator apparatus whose principle is the same as the example shown in FIG. 24. The two semicircular conductor patches 17 are capacitively coupled by chip capacitors 18 across the gap 16 and a chip resistance 34 provides a connection between the gate and drain, thereby establishing a phase condition for satisfying a negative resistance condition by positive feedback.
FIG. 26 shows another example of a radiating oscillator apparatus configuration in which the planar conductor patches serve as both a resonator and an electromagnetic wave output section (X. D. Resonator 1 and K. Chang, "Novel Active FET Circular Patch Antenna Arrays for Quasi-Optical Power Combining," IEEE Trans. Microwave Theory Tech., Vol. MTT-42, pp. 766 to 771, May 1994). In principle, this apparatus comprised by two circular conductor patches 17 placed in proximity with a high-frequency FET 12 therebetween is similar to that of the radiating oscillator apparatus of FIG. 24, with the circular conductor patches 17 forming a resonator. Other than the ability to adjust the distance of separation between the conductor patches and the conductor planar surface disposed under and parallel to the conductor patches, the configuration offers no freedom in terms of the ability to adjust the parameters of the radiating oscillator apparatus.
In order to build up oscillation and accumulate electromagnetic wave energy in the resonator, the feedback to the field effect transistor gate side has to be conducted at an appropriate phase and ratio. When the combination of feedback phase and amplitude meets the condition required of a negative resistance amplifier circuit as seen from the resonator, oscillation becomes possible and a high-frequency electromagnetic field is accumulated in the resonator. At this time, for a negative resistance circuit to be seen from the resonator, the condition of positive feedback condition to the transistor amplifier must be satisfied and, moreover, the securing of weak coupling between the resonator and free space is a basic requirement.
The radiating oscillator apparatuses of FIGS. 24, 25 and 26, in which a resonator is used that also functions as an antenna, are devised to enable adjustment of the condition of positive feedback to the high-frequency transistor by adjusting the capacitance. However, the method shown in FIG. 24 of adjusting the capacitance by varying the width of the narrow gap between the two rectangular conductor patches 15 does not allow the adjustment to be made with sufficient freedom. The method shown in FIG. 25 of using chip capacitors to couple the circular conductor patches 17 is not effective in the milliwave region without modification and thus is similarly deficient in terms of freedom of adjustment. Moreover, as already mentioned, other than the ability to adjust the distance of the separation between the conductor patches and the conductor planar surface disposed under and parallel to the conductor patches, the method of FIG. 26 also lacks adjustability.
Thus, none of the methods of FIGS. 24, 25 and 26 gives consideration to the matter of securing a weakly coupled state between the conductor patches, that is, the resonator, and free space, and neither do the methods make any disclosure regarding a way of realizing a weakly coupled state between free space and the resonator. The radiating oscillator apparatuses using resonators that also function as antennas shown in FIGS. 24, 25 and 26 therefore do not disclose a method for realizing an optimum oscillation state.
FIG. 27 shows a planar configuration of a micro- and millimeter wave radiating oscillator apparatus disclosed by the present inventors (JP-A Hei 9-220579). This apparatus comprises a pair of fan-shaped conductor patches 19 disposed with their pointed portions 20 in proximity and their arcuate portions on opposite sides, a high-frequency FET 12 disposed therebetween having a gate connected to one of the fan-shaped conductor patches 19, a drain connected to the fan-shaped other conductor patch 19 and a source connected to ground, a conductor planar surface disposed parallel to the surfaces of the fan-shaped conductor patches 19 and spaced therefrom by a separation that is between one-fifteenth and one-fifth the wavelength generated therefrom. The radius of each of the fan-shaped conductor patches 19 is about one-fourth the oscillation wavelength. Each fan-shaped conductor patch 19 is connected through a direct current bias line 11 to a separate direct current power source whose source is at ground potential.
The technology disclosed by FIG. 27 is superior to the prior art technologies in that it permits adjustment of the distance of the separation between the conductor patches 19 and the conductor planar surface, and in that there is freedom of adjustment of the angle of divergence .theta. of the fan-shaped conductor patches 19. Similarly to the radiating oscillator apparatus described with reference to FIG. 22 whose oscillation resonator also functions as an electromagnetic wave output section that employs Fabry-Perot resonator technology, the planar conductor patches of the radiating oscillator apparatus function both as a resonator and as an electromagnetic wave extraction section, thereby securing two controllable parameters required for optimization of oscillation conditions. In addition, it was expected to provide a planar radiating oscillation apparatus suitable for realizing high-efficiency power combining by mutual spatial phase synchronization of multiple such apparatus units arranged in a planar array.
However, the move to higher frequencies leading to finer device geometries, the increase in characteristic differentials among individual high-frequency transistors, the larger degree of error in the precision with which circuits and resonators are fabricated, the growing effect of non-uniformity of materials and other such factors made radiating oscillator apparatuses more susceptible to the effects of oscillation frequency variation. Further, along with the rise in the number of oscillators used in arrays, the demands on uniformity and the coupling strength requirements became increasingly rigorous. Thus, there has been a need to develop new technologies that enable the achievement and adjustment of more wideband frequency synchronization and stronger spatial coupling.
The Gaussian beam resonator is limited in application by the size of its aperture, which is several wavelengths or more. Moreover, it is by nature a high-Q resonator and, as such, is not appropriate for use in wideband frequency modulation, multifrequency sharing and other such applications. Further, although suitable for overlaying with a planar circuit, a resonator shaped like a plano-convex lens with one side comprised by a spherical mirror is relatively high in cost. Thus, a new solution is needed with respect to lowering costs.
By utilizing configuration technology findings obtained with respect to the beam radiating oscillator apparatus that as described in the foregoing uses a Gaussian-beam resonator, the present inventors were able to realize a high-efficiency radiating oscillator apparatus employing a planar resonator formed by fan-shaped conductor patches (JP-A Hei 9-220579). In accordance with this disclosure, it is possible to achieve a high-efficiency planar radiating oscillator apparatus for micro- to millimeter wave frequencies. From the standpoint of providing a planar radiating oscillation apparatus encompassing an array of oscillator apparatuses disposed in a single plane for readily enabling spatial coupling between the radiating oscillator apparatuses and realizing mutual spatial phase synchronization, of all the prior art structures, this was the one that had the greatest potential.
As mentioned, however, the move to higher frequencies leading to finer device geometries, differences between the characteristics of individual high-frequency transistors, the degree of error in the precision with which circuits and resonators are fabricated, non-uniformity of materials and other such error factors were tending to give rise to variation in the oscillation frequencies of individual radiating oscillator apparatuses. Further, along with the rise in the number of oscillators used in arrays, the demands with respect to uniformity of characteristics and coupling strength requirements became increasingly rigorous, giving rise to the need to develop new technologies that enable the achievement and adjustment of a wider range of synchronized frequencies and stronger spatial coupling.
The prior art technologies described in the foregoing have been unable to provide a planar radiating oscillator apparatus capable of simultaneously achieving high frequency output with high efficiency, wideband characteristics from microwave to the still higher frequency milliwave region, an array-based sharp beam radiation characteristic, high output through power combining and, in order to secure an enhanced degree of freedom for adaptively responding to application requirements for active beam shaping and the like, the ability to adjust the bandwidth of synchronizable frequencies and to adjust the spatial coupling strength, if desired.
The present invention was accomplished in the light of the foregoing circumstances and has as a main object to provide a planar radiating oscillator apparatus that if required is able to realize a broader synchronized frequency bandwidth as well as a higher spatial intercoupling strength, is adjustable and enables high-frequency output to be extracted into free space at high efficiency.
Another object of the invention is to provide a planar radiating oscillator apparatus for micro- and millimeter waves that is suitable for constituting and applying an array of a plurality of oscillator apparatuses of the invention in a single plane for realizing high-efficiency power combining by mutually synchronizing the array of oscillators.